324 THE ANTIQUITY OF MAN 
vertical In direction. The human teeth being relatively 
small, the dental part of the jaw has retreated backwards 
in the mouth. The muscular part, on the other hand, 
has been advanced ; there is now a prominent, or, at 
least, a well-marked chin. The genial pit and simian 
shelf seen in the ape's jaw are absent. In place of rising 
from a pit, the main muscles of the tongue — the right 
and left genio-glossus — arise from an elevation of bone 
bearing two tubercles. The genio-hyoid, in place of rising 
from the upper margin of the shelf of bone, springs from the 
lower part of the elevation which has filled up and replaced 
the pit, while the digastric muscles are attached to the 
lower border of the jaw just behind and below the chin. 
It will thus be seen that the simian and human 
mandible differ markedly in the region of the sym- 
physis or chin. The meaning of that difference will be 
discussed in a later chapter (p. 451). The type to which 
the Piltdown jaw belongs there can be no doubt ; both 
the genial pit and the simian plate are present. These 
are ape-like features. Dr Smith Woodward recognised 
them as such, and in his work of reconstructing the 
original form of the skull the presence of these simian 
features exercised a dominating influence. Hence, when 
he came to replace the missing parts of the jaws, the 
incisor and canine teeth, he followed simian rather than 
human lines. The teeth of man form a uniform series ; 
there is no break or diastema in front of, or behind, the 
canine teeth ; the canine tooth does not project prominently 
beyond its fellows. From the ape-like features of the 
chin it was inferred that projecting simian canine teeth 
must have been a characteristic of the Piltdown form of 
man. A massive canine tooth was therefore modelled ; 
not very projecting (see figs. 106, 108), thick and rather 
stumpy, its longest or front-to-back diameter being 14-5 
mm., its side-to-side, 10 mm. The diameters of such a 
tooth are equal to those of the canine of a male chimpan- 
zee, and far beyond the limits of the largest human 
canines known. As in the chimpanzee, a break or 
interval in the dental series was left both in front of and 
